Solid freeform fabrication (SFF) or layer manufacturing is a new rapid prototyping and manufacturing technology. A SFF system builds an object layer by layer or point by point under the control of a computer. The process begins with creating a Computer Aided Design (CAD) file to represent the desired object. This CAD file is converted to a suitable format, e.g. stereo lithography (.STL) format, and further sliced into a large number of thin layers with the contours of each layer being defined by a plurality of line segments connected to form vectors or polylines. The layer data are converted to tool path data normally in terms of computer numerical control (CNC) codes such as G-codes and M-codes. These codes are then utilized to drive a fabrication tool for building an object layer by layer.
The SFF technology has found a broad range of applications such as verifying CAD database, evaluating design feasibility, testing part functionality, assessing aesthetics, checking ergonomics of design, aiding in tool and fixture design, creating conceptual models and sales/marketing tools, generating patterns for investment casting, reducing or eliminating engineering changes in production, and providing small production runs. Although most of the prior-art SFF techniques are capable of making 3-D form models on a macroscopic scale, few are able to directly produce a microelectronic device or micro-electromechanical system (MEMS) that contains micron- or nano-scale functional elements.
In U.S. Pat. No. 4,665,492, issued May 12, 1987, Masters teaches part fabrication by spraying liquid resin droplets, a process commonly referred to as Ballistic Particle Modeling (BPM). The BPM process includes heating a supply of thermoplastic resin to above its melting point and pumping the liquid resin to a nozzle, which ejects small liquid droplets from different directions to deposit on a substrate. Patents related to the BPM technology can also be found in U.S. Pat. No. 5,216,616 (June 1993 to Masters), U.S. Pat. No. 5,555,176 (September 1996, Menhennett, et al.), and U.S. Pat. No. 5,257,657 (November 1993 to Gore). Sanders Prototype, Inc. (Merrimack, N.H.) provides inkjet print-head technology for making plastic or wax models. Multiple-inkjet based rapid prototyping systems for making wax or plastic models are available from 3D Systems, Inc. (Valencia, Calif.). Model making from curable resins using an inkjet print-head is disclosed by Yamane, et al. (U.S. Pat. No. 5,059,266, October 1991 and U.S. Pat. No. 5,140,937, August 1992) and by Helinski (U.S. Pat. No. 5,136,515, August 1992). Inkjet printing involves ejecting fine polymer or wax droplets from a print-head nozzle that is either thermally activated or piezo-electrically activated. The droplet size typically lies between 30 and 50 .mu.m, but could go down to 13 .mu.m. This implies that inkjet printing offers a part accuracy on the order of 13 .mu.m or worse which, for the most part, is not adequate for the fabrication of microelectronic devices.
Methods that involve deposition of metal parts from a steam of liquid metal droplets are disclosed in Orme, et al (e.g., U.S. Pat. No. 5,171,360) and in Sterett, et al. (U.S. Pat. No. 5,617,911). The method of Orme, et al involves directing a stream of a liquid material onto a collector of the shape of the desired product. A time dependent modulated disturbance is applied to the stream to produce a liquid droplet stream with the droplets impinging upon the collector and solidifying into a unitary shape. The method of Sterett, et al entails providing a supply of liquid metal droplets with each droplet being endowed with a positive or negative charge. The steam of liquid droplets is focused by passing these charged droplets through an alignment means, e.g., an electric field, to deposit on a target in a predetermined pattern. The deflection of heavy droplets of liquid metal by an electric field is not easy to accomplish. Further, a continuous supply of liquid metal droplets may make it difficult to prevent droplets from reaching "negative" regions (which are not portions of a cross-section of the object). A mask will have to be used to collect these un-desired droplets.
In U.S. Pat. No. 5,301,863 issued on Apr. 12, 1994, Prinz and Weiss disclose a Shape Deposition Manufacturing (SDM) system. The system contains a material deposition station and a plurality of processing stations (for mask making, heat treating, packaging, complementary material deposition, shot peening, cleaning, shaping, sand-blasting, and inspection). Each processing station performs a separate function such that when the functions are performed in series, a layer of an object is produced and is prepared for the deposition of the next layer. This system requires an article transfer apparatus, a robot arm, to repetitively move the object-supporting platform and any layers formed thereon out of the deposition station into one or more of the processing stations before returning to the deposition station for building the next layer. These additional operations in the processing stations tend to shift the relative position of the object with respect to the object platform. Further, the transfer apparatus may not precisely bring the object to its exact previous position. Hence, the subsequent layer may be deposited on an incorrect spot, thereby compromising part accuracy. The more processing stations that the growing object has to go through, the higher the chances are for the part accuracy to be lost. Such a complex and complicated process necessarily makes the over-all fabrication equipment bulky, heavy, expensive, and difficult to maintain. The equipment also requires attended operation.
The selected laser sintering or SLS technique (e.g., U.S. Pat. No. 4,863,538 issued in September 1989 to Deckard and U.S. Pat. No. 4,944,817 issued July 1990 to Bourell, et al.) involves spreading a full-layer of powder particles and uses a computer-controlled, high-power laser to partially melt these particles at desired spots. Commonly used powders include thermoplastic particles or thermoplastic-coated metal and ceramic particles. The procedures are repeated for subsequent layers, one layer at a time, according to the CAD data of the sliced-part geometry.
In a series of U.S. Patents (U.S. Pat. No. 5,017,317 in May 1991; U.S. Pat. No. 5,135,695 in August 1992; U.S. Pat. No. 5,169,579 in December 1992; U.S. Pat. No. 5,306,447 in April 1994; U.S. Pat. No. 5,611,883 in March 1997), Marcus and co-workers have disclosed a selected area laser deposition (SALD) technique for selectively depositing a layer of material from a gas phase to produce a part composed of a plurality of deposited layers. The SALD apparatus includes a computer controlling and directing a laser beam into a chamber containing the gas phase. The laser causes decomposition of the gas phase and selectively deposits material within the boundaries of the desired cross-sectional regions of the part. A major advantage of this technique is that it is capable of depositing a wide variety of materials to form an object on a layer by layer basis. The prior art SALD technique, however, is subject to the following shortcomings:
(1) Just like most of the prior-art layer manufacturing techniques, the SALD technique is largely limited to producing parts with homogeneous material compositions. Although, in principle, SALD allows for variations in the material composition from layer to layer, these variations can not be easily accomplished with the prior art SALD apparatus. For instance, upon completion of depositing a layer, the remaining gas molecules must be evacuated out of the build chamber, which is then filled with a second gas phase composition. This would be a slow and tedious procedure.
(2) The prior art SALD technique does not readily permit variations in the material composition from spot to spot in a given layer. This is due to the fact that the chamber is filled with a gas phase of an essentially uniform composition during the formation of a specific layer. In other words, the laser beam only decomposes one specific gas composition, leading to the deposition of a uniform-composition layer. In many applications (e.g., "direct writing" or deposition of a microelectronic device) material compositions vary as a function of spatial locations.
(3) The prior art SALD technique has poor resolution, precision or accuracy. The deposition spot size could not be smaller than the laser beam spot size, which is normally quite large. It is difficult to produce micron or sub-micron scale deposition spots with prior art SALD.
In U.S. Pat. No. 4,615,904 issued in October 1986, Ehrlich, et al. disclose a method of growing patterned films on a substrate in a deposition chamber. The method consists of the following steps: (1) pressurizing the chamber with a fluid medium to form a thin absorption layer on the substrate, (2) evacuating the chamber to remove excess fluid medium, (3) pre-nucleating portions of the substrate with a focused energy beam, (4) re-pressurizing the chamber with a fluid medium, and (5) inducing deposition of material from the liquid medium. This method permits growth of a patterned film with deposition occurring primarily on the pre-nucleated portions of the substrate. This method suffers from substantially the same drawbacks as with SALD.
Therefore, an object of the present invention is to provide an improved layer-additive process and apparatus for producing an object with high part accuracy.
Another object of the present invention is to provide a computer-controlled process and apparatus for producing a multi-material 3-D object on a layer-by-layer basis.
Still another object of the present invention is to provide a computer-controlled process and apparatus capable of producing multiple-layer microelectronic devices.
It is another object of this invention to provide a process and apparatus for building a CAD-defined object in which the material composition distribution can be predetermined.
Still another object of this invention is to provide a layer manufacturing technique that places minimal constraint on the range of materials that can be used in the fabrication of a 3-D object.